Investigators did find blood on a warning sign that was in an area between the railing and the enclosure. That area was off-limits to the public.
"Hard to speculate, but it leads me to believe the three young men may have been in part of the exhibit where Tatiana the tiger was," said zoo spokesman Sam Singer.
A 17-year-old died in the attack and his two friends were wounded.
The parents of the 17-year-old are considering filing a lawsuit against the zoo.